package cn.edu.scau.cmi.ema.util;

import org.apache.commons.math3.fitting.PolynomialCurveFitter;
import org.apache.commons.math3.fitting.WeightedObservedPoints;

import java.util.ArrayList;
import java.util.List;

interface CurveFitting {
	public Object run(List<Object> params) throws Exception;

	public List<Object> getParams();

	public void printResult(Object result);
}

class CurveFittingImpl implements CurveFitting {
	public CurveFittingImpl() {
		System.out.print("本算例用于计算多项式曲线拟合。正在初始化 计算数据(" + arrayLength + "点, " + degree + "阶)... ...");
		inputDataX = new double[arrayLength];
		// inputDataX = new double[] {1, 2, 3, 4, 5, 6, 7};
		inputDataY = new double[inputDataX.length];
		double[] factor = new double[degree + 1]; // N阶多项式会有N+1个系数，其中之一为常数项
		for (int index = 0; index < factor.length; index++) {
			factor[index] = index + 1;
		}
		for (int index = 0; index < inputDataY.length; index++) {
			inputDataX[index] = index * 0.00001;
			inputDataY[index] = calcPoly(inputDataX[index], factor); // y = sum(x[n) * fact[n])
			// System.out.print(inputDataY[index] + ", ");
		}
		points = new WeightedObservedPoints();
		for (int index = 0; index < inputDataX.length; index++) {
			points.add(inputDataX[index], inputDataY[index]);
		}
		System.out.println("初始化完成");
	}

	@Override
	public List<Object> getParams() {
		List<Object> params = new ArrayList<Object>();
		params.add(points);
		return params;
	}

	@Override
	public Object run(List<Object> params) throws Exception {
		PolynomialCurveFitter fitter = PolynomialCurveFitter.create(degree);
		WeightedObservedPoints points = (WeightedObservedPoints) params.get(0);
		double[] result = fitter.fit(points.toList());
		return result;
	}

	@Override
	public void printResult(Object result) {
		for (double data : (double[]) result) {
			System.out.println(data);
		}
	}

	private double calcPoly(double x, double[] factor) {
		double y = 0;
		for (int deg = 0; deg < factor.length; deg++) {
			y += Math.pow(x, deg) * factor[deg];
		}
		return y;
	}

	private double[] inputDataX = null;
	private double[] inputDataY = null;
	private WeightedObservedPoints points = null;
	private final int arrayLength = 200000;
	private final int degree = 10; // 阶数
}

public class CurverFitUtilTest {
	public CurverFitUtilTest() {
	}

	/**
	 * 计算指定对象的运行时间开销。
	 *
	 * @param curveFitting 指定被测对象。
	 * @return 返回sub.run的时间开销，单位为s。
	 * @throws Exception
	 */
	public double calcTimeCost(CurveFitting curveFitting) throws Exception {
		List<Object> params = curveFitting.getParams();
		long startTime = System.nanoTime();
		Object result = curveFitting.run(params);
		long stopTime = System.nanoTime();
		curveFitting.printResult(result);
		System.out.println("start: " + startTime + " / stop: " + stopTime);
		double timeCost = (stopTime - startTime) * 1.0e-9;
		return timeCost;
	}

	public static void main(String[] args) throws Exception {
		CurverFitUtilTest tcc = new CurverFitUtilTest();
		double timeCost;
		System.out.println("--------------------------------------------------------------------------");
		timeCost = tcc.calcTimeCost(new CurveFittingImpl());
		System.out.println("time cost is: " + timeCost + "s");
		System.out.println("--------------------------------------------------------------------------");
	}
}
